1. Field of the Invention
The present invention is one relating to a semiconductor device and a method for manufacturing the same, and more particularly to a semiconductor device having a fin-shaped semiconductor portion and a method for manufacturing the same.
2. Description of the Background Art
In recent years, miniaturization of transistors is performed in order to advance high integration of LSI, a semiconductor device. However, conventional planar transistors face their physical limitation, and the development of new transistor structures other than planar transistors is necessary for miniaturization of transistors. One of newly developed transistor structures is a fin-type transistor of a vertical structure, which is disclosed in Japanese Patent Application Laid-Open Nos. 2005-294789 and 2007-35957.
Regarding the fin-type transistor, a technique of forming this transistor on a bulk silicon wafer or an SOI (Silicon on Insulator) wafer is generally known. In particular, it is known that a fin-type transistor formed on an SOI wafer is advantageous for high integration and, in addition, can suppress the short channel effects. In contrast, although a fin-type transistor formed on a bulk silicon wafer has an advantage of allowing the fin-type transistor to be formed at low cost, it requires optimization of impurity profiles in a silicon layer under a fin-shaped semiconductor portion and suppression of the short channel effects is difficult.
A fin-type transistor is advantageous for high integration of a semiconductor device, and a fin-type transistor formed on an SOI wafer has the effect of suppressing short channel effects. However, the fin-type transistor has difficulty in element formation from the viewpoint of processes, compared to a planar transistor. This causes various problems with the fin-type transistor. In particular, processing a fin-shaped semiconductor portion and a gate electrode is difficult, and thus forming the fin-shaped semiconductor portion and the gate electrode with high precision is an important factor for improvement of characteristics of the fin-type transistor. It is also desired that variations in characteristics among elements of the fin-type transistor are suppressed.